Continuing with the alternative energy series, this week’s blog will examine another newly expanding area in green alternatives: tidal energy, or the energy created from the ocean’s waves. Waves are a form of energy which lift water up as it moves along. Tidal energy seems like a very viable alternative option for one main reason: one cubic meter of water weighs one ton, and while a cubic meter of water is not a substantial amount, the smallest of waves can lift thousands of cubic meters of water as they move.i That’s similar to lifting thousands of cars in one fluid motion. Waves are mainly generated from wind out at sea, similar to the ripples in a pond. However, in the ocean where there are deeper waters and nothing inhibiting them, the ripples are able to continuously grow as they approach the shore. The varying force and size of ocean waves is also largely affected by the gravitational pull of the moon. The power from the moon’s gravitational field “pulls” the ocean water away from the Earth, so the ocean that is facing the moon will bulge toward the moon while the ocean facing away from the moon will bulge in the opposite direction due to the Earth’s own gravitational pull. The rotation of the Earth, coupled with this effect is what causes a change in ocean tides.
Tidal Energy in Motion
There are currently two possible ways to capture the energy seen in ocean waves. The first, and more common method, is a large underwater turbine system. These systems are designed to capture the kinetic motion energy of the ebbing and surging of ocean tides in order to produce electricity. Similar to wind turbines, the ocean turbine systems generate energy when the waves spin the turbines; however ocean currents can generate more electricity than wind because ocean water has a higher density than air and applies a greater force on the turbine blades. The second method to capture ocean tidal energy is a system known as a tidal barrage or dam. The barrage is placed across an estuary that captures the potential energy generated by the change in height (or head) between high and low tides.ii As the tide alternates in and out the water flows through tunnels that are placed within the dam. The varying motion of the water is used to compress air through a pipe which then turns a turbine and generates electricity. The first full-scale application for a tidal engineering generator to be implemented was recently approved in Wales, with plans to have full deployment by 2015, and a demonstrational period starting as early as 2014.iii
A proposed idea that recently received funding to progress is a small kite known as “Deep Green”. The kite has a 39-foot wingspan and has a 328-foot cable connecting it to the ocean floor. The advantage to the kite design is that it operates at greater depths where the currents are slower. Once anchored, Deep Green can be steered similar to the high altitude kites used to capture wind energy, and can capture energy at 10 times the speed of actual stream velocity. One deep sea kite is predicted to generate 500 kilowatts of power.iv
The long term application for all alternative energy sources is to replace the dependence on fossil fuels and move toward a sustainable and environmental society. With current advancements in tidal energy engineering, it is likely to assume that turbines will not only be paced in open fields to catch energy from the winds, but on the ocean floor as well.
i Planet Green Discovery.com “Oceanography” October 8, 2012
ii Pembina Institute “Energy Source: Tidal Power” 2012
iii Hill, Joshua CleanTechnical “Wales First Full-Scale Tidal Energy Generator Receives Funding” May 8, 2013
iv Laut, Emily Science NBC News “Underwater Kite Captures Tidal Energy”, May 10, 2011